Perennial woody plants such as deciduous fruit trees and grape vines require chilling temperatures between growing seasons to properly bear a commercially acceptable fruit yield during the growing season. Specifically, the plants develop a resting bud at the conclusion of the growing season that better survives chilling temperatures between growing seasons. This bud stage is known as dormancy. In order for dormancy to be broken and plant growth to resume, a threshold amount of chilling is required. Effective chilling is based on both the duration of chilling and the temperature of the chilling period. This is normally followed by elevated temperatures that break dormancy and lead to synchronous flowering and fruit development. This breaking of dormancy in perennial woody plants is known as bud break.
In warmer climates, perennial woody plants do not receive sufficient chilling, and without chemical intervention to break dormancy, asynchronous bud break, flowering and fruit set may significantly reduce fruit yield. The most commercially successful bud dormancy breaking chemical is hydrogen cyanamide. Hydrogen cyanamide is the active agent in Dormex® (Dormex is a registered trademark of and available from AlzChem AG, Germany). In addition to compensating for a lack of chilling, hydrogen cyanamide has been used to initiate earlier bud break and more synchronous bud break leading to better fruit yields. However, hydrogen cyanamide is highly toxic and has been shown to cause adverse human health effects from contact with the skin and/or mucous membranes. See Schep et al.: The adverse effects of hydrogen cyanamide on human health: an evaluation of inquiries to the New Zealand National Poisons Centre. Clin Toxicol (Phila). 2009 47(1):58-60. Moreover, high rates of hydrogen cyanamide are associated with in-season phytotoxicity and long-term decline in vine health and bearing.
Thidiazuron, 1-Phenyl-3-(1,2,3-thiadiazol-5-yl)urea, is another chemical that has been used to break bud dormancy. Thidiazuron has been reported to break dormancy in apples, plums, and grapes. See Wang S Y, et al.: Breaking bud dormancy in apple with a plant bioregulator, thidiazuron, Phytochem, 1986 January, 25(2), 311-317; and Alvarado R H, et al.: Thidiazuron, flower budbreak and ovary dimensions in Japanese plum (Prunus salicina L.) “Shiro”, Agrociencia, 2002 34(3) 321-327. However, thidiazuron is less-effective and not as reproducible as a dormancy beaker in the field as hydrogen cyanamide. Moreover, it may be phytotoxic at high concentrations.
Nitrogen-containing fertilizers are used to enhance plant growth in most plant species. Nitrogen fertilizers have also been shown to promote bud break and bud break synchrony in apples, cherries and grapes. Hawerroth F J, et al.: Erger and calcium nitrate concentration for budbreak induction in apple trees, Acta Hort., 2010 August, 872(32), 239-244. However, nitrogen fertilizers are not as effective or consistent as hydrogen cyanamide at breaking bud dormancy.
Accordingly, there is a need in the art for a composition that can break bud dormancy as well or better than hydrogen cyanamide but without causing negative plant or animal health issues.